Summary
We propose to adopt a new airworthiness directive (AD) for the MDHI Model MD900 helicopters with certain main rotor blade (MRB) retention bolts (bolts) installed. This proposed AD would require a daily check of the position of each bolt and would also require a daily check and a repetitive inspection for a gap in each bolt. The proposed AD would also require, if necessary, removing and inspecting the bolt for a crack and replacing any cracked bolt with an airworthy bolt. This proposed AD is prompted by multiple reports of in-service bolt failures. The proposed actions are intended to prevent failure of a bolt, which could lead to loss of MRB structural integrity and subsequent loss of control of the helicopter.